to rain
The German word 'regnen' is a verb that means 'to rain'. It is used in the same way as its English counterpart, for example: 'Es regnet heute.' (It's raining today.) Note that unlike in English, German does not use an auxiliary verb with 'regnen'. So, 'It is raining' in German is simply 'Es regnet'.
It will rain this evening.
This sentence is an example of using 'regnen' to describe future occurrences of rain. In this instance, the phrase 'Es wird heute Abend regnen' directly translates to 'It will rain this evening'.
I hope it will not rain.
In the sentence 'Ich hoffe, es wird nicht regnen', regnen is used to express a hope or desire about the weather. The sentence translates directly as 'I hope it will not rain'.
It rained all night yesterday.
The phrase 'Es hat gestern die ganze Nacht geregnet' uses 'regnen' in past tense ('geregnet') to describe a past occurrence. The sentence translates to 'It rained all night yesterday'.